DNA, Chromosomes, Mitosis & Meiosis — Genetics Fundamentals

DNA and Chromosomes

DNA is the biomolecule that contains genetic information to make proteins in the cell.

The chromosomes are composed of chromatin (DNA + protein).

Before cell division the DNA is duplicated. Each chromosome is formed by two chromatids joined together.

Karyotype and Genome

Karyotype: chromosome set ordered by pairs. Humans have 23 pairs.

Genome: the complete set of genes.

Genes and Genetic Information

A gene is a segment of DNA containing information to produce a given necessary protein. Genes together make up the genome.

Cell Cycle and Division

Cellular division is the process by which a cell is divided into two daughter cells.

Interphase

Interphase is the stage of growth: the cell increases in size, the cytoplasm grows, and routine cellular functions occur.

Cell Division: Mitosis and Cytokinesis

Cell division includes mitosis and cytokinesis — mitosis divides the nucleus; cytokinesis divides the cytoplasm and separates the daughter cells.

Mitosis

Mitosis is the division of the nucleus and the distribution of chromosomes (prophase, metaphase, anaphase and telophase). It takes place in most somatic cells to grow and repair tissue, producing cells genetically identical to the parent and with the same chromosome number.

• Phases: prophase, metaphase, anaphase, telophase.

Cytokinesis

Cytokinesis — in animals: contractile microfilaments produce a constriction of the mother cell until it becomes two independent daughter cells.

Meiosis

Meiosis consists of two consecutive cell divisions. The second division resembles mitosis but occurs without intervening DNA replication. Four cells are formed with half the chromosomes of the mother cell. This only takes place during the formation of gametes (haploid). Sexual reproduction produces gametes with half the chromosomes and new combinations of genes.

Reproduction and Inheritance

Reproduction is the capacity of cells (or organisms) to produce offspring like themselves.

Genetic Terms

• Homozygous — both alleles of a homologous pair are the same.
• Heterozygous — the two alleles are different.
• Genotype — the set of genes that an individual has.
• Phenotype — the observable appearance of an individual.
• Diploid — having two sets of chromosomes.
• Haploid — having only one set of chromosomes.

Summary of Cell Division Processes

Mitosis is the equitable distribution of hereditary material characteristic of eukaryotic cells. It usually concludes with the formation of two separate nuclei followed by partition of the cytoplasm to form two daughter cells. Mitosis produces genetically identical cells and is the foundation of growth, repair and asexual reproduction.

Meiosis produces genetically distinct cells and, combined with fertilization, contributes to genetic variation in offspring.